ß-Cyclodextrin-Mediated Enantioselective Photochemical Electrocyclization of 1,3-Dihydro-2H-azepin-2-one.

The photochemical electrocyclization reaction of the title compound in the presence of ß-cyclodextrin was examined in different conditions. No enantioselectivity was observed in solution, but solid-state reactions of a 1:1 complex as a suspension or a thin film, followed by reduction, provided (1R,5R)-2-azabicyclo[3.2.0]heptan-3-one in isolated yields up to 79% and with ee values up to 45%.

Conformational Effects through Hydrogen Bonding in a Constrained γ-Peptide Template: From Intraresidue Seven-Membered Rings to a Gel-Forming Sheet Structure.

A series of three short oligomers (di-, tri-, and tetramers) of cis-2-(aminomethyl)cyclobutane carboxylic acid, a γ-amino acid featuring a cyclobutane ring constraint, were prepared, and their conformational behavior was examined spectroscopically and by molecular modeling. In dilute solutions, these peptides showed a number of low-energy conformers, including ribbonlike structures pleated around a rarely observed series of intramolecular seven-membered hydrogen bonds. In more concentrated solutions, these interactions defer to an organized supramolecular assembly, leading to thermoreversible organogel formation notably for the tripeptide, which produced fibrillar xerogels. In the solid state, the dipeptide adopted a fully extended conformation featuring a one-dimensional network of intermolecularly H-bonded molecules stacked in an antiparallel sheet alignment. This work provides unique insight into the interplay between inter- and intramolecular H-bonded conformer topologies for the same peptide template.